1. Field of the Invention
This invention relates to a process for preparing ultra-high molecular weight poly(alpha-olefin) (hereinafter. UHMWPO) multi-filament yarns and the yarns produced thereby.
2. Description of the Prior Art
UHMWPO multi-filament yarns have been produced possessing high tensile properties such as tenacity, tensile modulus and energy-to-break. The yarns are useful in applications requiring impact absorption and ballistic resistance such as body armor, helmets, breast plates, helicopter seats, spall shields; composite sports equipment such as kayaks, canoes bicycles and boats; and in fishing line, sails, ropes, sutures and fabrics.
Ultra-high molecular weight poly(alpha-olefins) include polyethylene, polypropylene, poly(butene-1), poly(4-methyl-pentene-1), their copolymers, blends and adducts. Multi-filament “gel spun” ultra-high molecular weight polyethylene (UHMWPE) yarns are produced, for example, by Honeywell International Inc. The gel-spinning process discourages the formation of folded chain molecular structures and favors formation of extended chain structures that more efficiently transmit tensile loads.
The first description of the preparation and drawing of single UHMWPE filaments in the gel state was by P. Smith. P. J. Lemstra, B. Kalb and A. J. Pennings, Poly. Bull., 1, 731 (1979). Single filaments of UHMWPE were spun from solution and drawn while evaporating the solvent. Further descriptions of the drawing of polyethylene filaments containing substantial concentrations of solvent such as decalin or wax are described, for example, in P. Smith and P. J. Lemstra, Macromol. Chem., 180, 2983 (1979): J. Matl. Sci., 15, 505 (1980): and in the following patents and patent applications: GB 2,042,414A; GB 2,051,667B, U.S. Pat. Nos. 4,411,854: 4,422,993; 4,430,383: 4,436,689; EP 0 077.590; U.S. Pat. Nos. 4,617,233; 4,545,950; 4,612,148; 5,246,657; 5,342,567; EP 0 320,188 A2 and JP-A-60/5264, U.S. Pat. No. 4,422,993 discloses that higher draw ratios can be achieved in drawing solvent-containing filaments than with filaments containing little or no solvent and that drawing of solvent-containing filaments results in higher tensile properties.
The drawing of gel-spun high strength polyethylene filaments in essentially a diluent-free state was first described by B. Kalb and A. J. Pennings, Poly. Bull., 1, 871 (1979). Single filaments were spun from dodecane solution and simultaneously dried and stretched in a heated tube under an increasing temperature of 100 to 148° C. A dried filament of about 10 g/d (9 g/dtex) tenacity was then re-stretched at 153° C. to a tenacity of about 29 g/d (26.1 g/dtex).
Further descriptions of the drawing of gel-spun polyethylene filaments in an essentially diluent-free state are described, for example, in B. Kalb and A. J. Pennings, Polymer, 21, 3 (1980); J. Smook et. al, Poly. Bull., 2, 775 (1980); P. Smith et el., J. Poly Sci., Poly Phys. Ed., 19, 877 (1981); J. Smook and A. J. Pennings, J. Appl. Poly. Sci., 27, 2209 (1982), J. Matl. Sci., 19, 31 (1984), J. Matl. Sci., 19, 3443 (1984): J. P. Penning et al., Poly. Bull., 31, 243 (1993); Japan Kokai Patent Publication 238416-1995; and in the following U.S. Pat. Nos. 4,413,110; 4,536,536; 4,551,296; 4,663,101; 5,032,338; 5,286,435; 5,578,374; 5,736,244; 5,741,451; 5,958,582; 5,972,498; and 6,448,359.
More recent processes (see, e.g., U.S. Pat. Nos. 4,551,296; 4,663,101; 6,448,659; and 6,969,553) describe drawing all three of the solution filaments, the gel filaments and the solvent-free filaments. Yet another recent drawing processes is described in co-pending United States published application 20050093200. The disclosures of the aforementioned U.S. Pat. Nos. 4,551,296, 4,663,101, 5,741,451, 6,448,659, and 6,969,553 and United States published application 20050093200 are hereby expressly incorporated by reference to the extent not incompatible herewith.
The first description of the preparation and drawing of multi-filament yarns of UHMWPO was in U.S. Pat. No. 4,413,110. The first process where essentially diluent-free dry yarns were drawn in-line with spinning and then were redrawn off-line was described in U.S. Pat. No. 5,741,451. It will be understood that the terms “in-line” and “off-line” refer to a continuous sequential operation and a discontinuous sequential operation respectively.
Although each of the foregoing documents represented an advance in the state of the art, it would be desirable to provide a process for preparing UHMWPO multi-filament yarns having improved tensile properties at higher productivity.